This invention relates to a shutter opening and closing mechanism for electrographic apparatus.
Various kinds of electrographic apparatus have been known which make use of a photosensitive screen and in which at first the photosensitive screen is uniformly charged and then a manuscript image is exposed and scanned so as to form a first electrostatic latent image on the photosensitive screen and a flow of corona ions is modulated to transfer the first electrostatic latent image onto a dielectric coated record sheet so as to produce a second electrostatic latent image on the dielectric coated record sheet. Such electrographic apparatus has the advantage that it is possible to reproduce a plurality of copies on the basis of the first electrostatic latent image produced on the photosensitive screen by only one exposure and scanning of the manuscript image, and that, in the case of reproducing a plurality of copies after the first electrostatic latent image has been produced on the photosensitive screen, it is possible to omit the above mentioned steps of uniformly charging the photosensitive screen, exposing and scanning the manuscript image and effecting movements of a reciprocating scanning means such as a reciprocating carriage on which is placed a manuscript or a reciprocating light source. For this purpose, the first electrostatic latent image produced on the photosensitive screen must effectively be maintained for a long time.
A photosensitive screen of a four layer construction has also been known. Such photosensitive screen is composed of an electrically conductive core coated on one side with an insulating layer and electrically conductive layer in the order as mentioned above and coated on the other side with a photoconductive layer. In such photosensitive screen, the first electrostatic latent image is produced on its photoconductive layer. After the first electrostatic latent image has been produced on the photoconductive layer of the photosensitive screen, if the photosensitive screen is exposed again, the first electrostatic latent image corresponding to the manuscript image and produced on the photoconductive layer becomes decayed or eliminated. As a result, in the step of transferring the first electrostatic latent image produced on the photosensitive screen onto the record sheet, if the manuscript placed on the carriage is replaced for another manuscript under such condition that the carriage is not sufficiently covered against the exterior light, the first electrostatic latent image produced on the photosensitive screen becomes decayed or eliminated by the exterior light. Thus, it is impossible to sufficiently shorten the total time of reproducing a plurality of copies.
In order to eliminate the above mentioned drawback, an electrographic apparatus provided with a shutter has been proposed. In such electrographic apparatus, in a light path for projecting a manuscript image onto a photosensitive screen is arranged a shutter adapted to be opened only when a first electrostatic latent image is produced on the photosensitive screen. In such electrographic apparatus, if the first electrostatic latent image corresponding to the manuscript image is produced on the photosensitive screen, such first electrostatic latent image can be effectively maintained for a long time without being decayed nor eliminated even during the intervals of time in which a plurality of copies are reproduced on the basis of the first electrostatic latent image produced on the photosensitive screen. In addition, the manuscript placed on the carriage can be replaced by another manuscript and it is possible to prepare for the next copying operation.